In recent years, the trend to eliminate the use of hazardous materials is becoming increasingly stringent, out of concerns about environmental problems. For example, restrictions such as “Restriction on Hazardous Substances (RoHS)” are implemented in Europe. According to this restriction, it is demanded to guarantee that specific hazardous substances are not contained in the material and components of a product. Among the substances restricted in Europe, chromium is demanded to be under different management depending on the valency, and only hexavalent chromium in products is defined as an object of restriction. However, since chromium has a nature that the valency is changed by an oxidation-reduction reaction, there is a demand for a pretreatment method for extracting recovering only hexavalent chromium with high yield, without changing its valency.
In the case of the water-soluble hexavalent chromium compound in a polymer, JP-A 2006-132979(KOKAI) discloses that hexavalent chromium dissolve into the organic acid salt from the pulverized polymer using supersonic wave.
Furthermore, JP-A 2008-232748 (KOKAI) suggests another method. When a polymer that dissolve in water-soluble organic solutions, it dissolve into a water-soluble organic solution then adding an aqueous alkali solution to it. Thus, hexavalent chromium is extracted by dissolving in aqueous alkali solution.